When your body temperature drops, your heart, nervous system and other organs can't work normally. Left untreated, hypothermia can eventually lead to complete failure of your heart and respiratory system and to death.

Hypothermia is most often caused by exposure to cold weather or immersion in a cold body of water. Primary treatments for hypothermia are methods to warm the body back to a normal temperature.

Shivering is likely the first thing you'll notice as the temperature starts to drop because it's your body's automatic defense against cold temperature — an attempt to warm itself.

Confusion and poor decision-making, such as trying to remove warm clothes

Drowsiness or very low energy

Lack of concern about one's condition

Progressive loss of consciousness

Weak pulse

Slow, shallow breathing

Someone with hypothermia usually isn't aware of his or her condition because the symptoms often begin gradually. Also, the confused thinking associated with hypothermia prevents self-awareness. The confused thinking can also lead to risk-taking behavior.

Hypothermia in infants

Typical signs of hypothermia in an infant include:

Bright red, cold skin

Very low energy

A weak cry

Hypothermia not necessarily related to the outdoors

Hypothermia isn't always the result of exposure to extremely cold outdoor temperatures. An older person may develop mild hypothermia after prolonged exposure to indoor temperatures that would generally be fine for a younger or healthier adult. This can occur in a poorly heated home or in an air-conditioned home. Signs and symptoms of this type of hypothermia may not be as obvious.

When to see a doctor

Call 911 or your local emergency number if you see someone with signs of hypothermia or if you suspect a person has had unprotected or prolonged exposure to cold weather or water.

If possible take the person inside, moving them carefully and slowly. Jarring movements can trigger dangerous irregular heartbeats. Carefully remove wet clothing, and cover him or her in layers of blankets while you wait for emergency help to arrive.

Hypothermia occurs when your body loses heat faster than it produces it. The most common causes of hypothermia are exposure to cold-weather conditions or cold water. But prolonged exposure to any environment colder than your body can lead to hypothermia if you aren't dressed appropriately or can't control the conditions.

Specific conditions leading to hypothermia include:

Wearing clothes that aren't warm enough for weather conditions

Staying out in the cold too long

Unable to get out of wet clothes or move to a warm, dry location

Accidental falls in water, as in a boating accident

Inadequate heating in the home, especially for older people and infants

Air conditioning that is too cold, especially for older people and infants

How your body loses heat

The mechanisms of heat loss from your body include the following:

Radiated heat. Most heat loss is due to heat radiated from unprotected surfaces of your body.

Direct contact. If you're in direct contact with something very cold, such as cold water or the cold ground, heat is conducted away from your body. Because water is very good at transferring heat from your body, body heat is lost much faster in cold water than in cold air. Similarly, heat loss from your body is much faster if your clothes are wet, as when you're caught out in the rain.

Wind. Wind removes body heat by carrying away the thin layer of warm air at the surface of your skin. A wind chill factor is important in causing heat loss.

A number of factors can increase the risk of developing hypothermia:

Older age. Older adults are more vulnerable to hypothermia for a number of reasons. The body's ability to regulate temperature and to sense cold may lessen with age.

Older people are also more likely to have a medical condition that affects temperature regulation. Some older adults may not be able to communicate when they are cold or may not be mobile enough to get to a warm location.

Very young age. Children lose heat faster than adults do. Children have a larger surface area-to-weight ratio than adults do, making them more prone to heat loss.

Children may also ignore the cold because they're having too much fun to think about it. And they may not have the judgment to dress properly in cold weather or to get out of the cold when they should. Infants may have a special problem with the cold because they have less efficient mechanisms for generating heat.

Mental problems. People with a mental illness, dementia or another condition that interferes with judgment may not dress appropriately for the weather or understand the risk of cold weather. People with dementia may wander from home or get lost easily, making them more likely to be stranded outside in cold or wet weather.

Alcohol and drug use. Alcohol may make your body feel warm inside, but it causes your blood vessels to dilate, or expand, resulting in more rapid heat loss from the surface of your skin. The body's natural shivering response is diminished in people who've been drinking alcohol. In addition, the use of alcohol or recreational drugs can affect your judgment about the need to get inside or wear warm clothes in cold weather conditions. If a person is intoxicated and passes out in cold weather, he or she is likely to develop hypothermia.

Medications. A number of drugs — including certain antidepressants, antipsychotics, narcotic pain medications and sedatives — can change the body's ability to regulate its temperature.

People who develop hypothermia because of exposure to cold weather or cold water are also vulnerable to other cold-related injuries, including:

Freezing of body tissues (frostbite)

Decay and death of tissue resulting from an interruption in blood flow (gangrene)

The diagnosis of hypothermia is usually apparent based on a person's physical signs and the conditions in which the person with hypothermia became ill or was found. Blood tests also can help confirm hypothermia and its severity.

A diagnosis may not be readily apparent, however, if the symptoms are mild, as when an older person who is indoors has symptoms of confusion, lack of coordination and speech problems. In such cases, an exam may include a temperature reading with a rectal thermometer that reads low temperatures.

Seek immediate medical attention for anyone who appears to have hypothermia. Until medical help is available, follow these hypothermia treatment guidelines.

First-aid care

Be gentle. When you're helping a person with hypothermia, handle him or her gently. Limit movements to only those that are necessary. Don't massage or rub the person. Excessive, vigorous or jarring movements may trigger cardiac arrest.

Move the person out of the cold. Move the person to a warm, dry location if possible. If you're unable to move the person out of the cold, shield him or her from the cold and wind as much as possible.

Cover the person with blankets. Use layers of dry blankets or coats to warm the person. Cover the person's head, leaving only the face exposed.

Insulate the person's body from the cold ground. If you're outside, lay the person on his or her back on a blanket or other warm surface.

Monitor breathing. A person with severe hypothermia may appear unconscious, with no apparent signs of a pulse or breathing. If the person's breathing has stopped or appears dangerously low or shallow, begin CPR immediately if you're trained.

Share body heat. To warm the person's body, remove your clothing and lie next to the person, making skin-to-skin contact. Then cover both of your bodies with blankets.

Provide warm beverages. If the affected person is alert and able to swallow, provide a warm, sweet, nonalcoholic, noncaffeinated beverage to help warm the body.

Use warm, dry compresses. Use a first-aid warm compress (a plastic fluid-filled bag that warms up when squeezed) or a makeshift compress of warm water in a plastic bottle or a dryer-warmed towel. Apply a compress only to the neck, chest wall or groin.

Don't apply a warm compress to the arms or legs. Heat applied to the arms and legs forces cold blood back toward the heart, lungs and brain, causing the core body temperature to drop. This can be fatal.

Don't apply direct heat. Don't use hot water, a heating pad or a heating lamp to warm the person. The extreme heat can damage the skin or, even worse, cause irregular heartbeats so severe that they can cause the heart to stop.

Medical treatment

Depending on the severity of hypothermia, emergency medical care for hypothermia may include one of the following interventions to raise the body temperature:

Blood rewarming. Blood may be drawn, warmed and recirculated in the body. A common method of warming blood is the use of a hemodialysis machine, which is normally used to filter blood in people with poor kidney function. Heart bypass machines also may need to be used.

Warm intravenous fluids. A warmed intravenous solution of salt water may be injected into a vein to help warm the blood.

Airway rewarming. The use of humidified oxygen administered with a mask or nasal tube can warm the airways and help raise the temperature of the body.

Irrigation. A warm saltwater solution may be used to warm certain areas of the body, such as the area around the lungs (pleura) or the abdominal cavity (peritoneal cavity).

Staying warm in cold weather

Before you or your children step out into cold air, remember the advice that follows with the simple acronym COLD — cover, overexertion, layers, dry:

Cover. Wear a hat or other protective covering to prevent body heat from escaping from your head, face and neck. Cover your hands with mittens instead of gloves. Mittens are more effective than gloves because mittens keep your fingers in closer contact.

Overexertion. Avoid activities that would cause you to sweat a lot. The combination of wet clothing and cold weather can cause you to lose body heat more quickly.

Dry. Stay as dry as possible. Get out of wet clothing as soon as possible. Be especially careful to keep your hands and feet dry, as it's easy for snow to get into mittens and boots.

Keeping children safe outdoors

To help prevent hypothermia when children are outside in the winter:

Dress infants and young children in one more layer than an adult would wear in the same conditions

Bring children indoors if they start shivering — that's the first sign that hypothermia is starting

Have children come inside frequently to warm themselves when they're playing outside

Don't let babies sleep in a cold room

Winter car safety

Whenever you're traveling during bad weather, be sure someone knows where you're headed and at what time you're expected to arrive. That way, if you get into trouble on your way, emergency responders will know where to look for your car.

It's also a good idea to keep emergency supplies in your car in case you get stranded. Supplies may include several blankets, matches, candles, a clean can where you can melt snow into drinking water, a first-aid kit, dry or canned food, a can opener, tow rope, booster cables, compass, and a bag of sand or kitty litter to spread for traction if you're stuck in the snow. Travel carrying a cellphone if possible.

If you're stranded, put everything you need in the car with you, huddle together and stay covered. Run the car for 10 minutes each hour to warm it up. Make sure a window is slightly open and the exhaust pipe isn't covered with snow while the engine is running.

Drinking alcohol

Take the following precautions to avoid alcohol-related risks of hypothermia.

Don't drink alcohol:

If you're going to be outside in cold weather

If you're boating

Before going to bed on cold nights

Cold-water safety

Water doesn't have to be extremely cold to cause hypothermia. Any water that's colder than normal body temperature causes heat loss. The following tips may increase your survival time in cold water if you accidentally fall in:

Wear a life jacket. If you plan to ride in a watercraft, wear a life jacket. A life jacket can help you stay alive longer in cold water by enabling you to float without using energy and by providing some insulation. Keep a whistle attached to your life jacket to signal for help.

Get out of the water if possible. Get out of the water as much as possible, such as climbing onto a capsized boat or grabbing onto a floating object.

Don't attempt to swim unless you're close to safety. Unless a boat, another person or a life jacket is close by, stay put. Swimming will use up energy and may shorten survival time.

Position your body to minimize heat loss. Use a body position known as the heat escape lessening position (HELP) to reduce heat loss while you wait for assistance. Hold your knees to your chest to protect the trunk of your body. If you're wearing a life jacket that turns your face down in this position, bring your legs tightly together, your arms to your sides and your head back.

Huddle with others. If you've fallen into cold water with other people, keep warm by facing each other in a tight circle.

Don't remove your clothing. While you're in the water, don't remove clothing because it helps to insulate you from the water. Buckle, button and zip up your clothes. Cover your head if possible. Remove clothing only after you're safely out of the water and can take measures to get dry and warm.

Help for at-risk people

For people most at risk of hypothermia — infants, older adults, people who have mental or physical problems, or people who are homeless — community outreach programs and social support services can be of great help. If you're at risk or know someone at risk, contact your local public health office for available services, such as the following:

Assistance for paying heating bills

Check-in services to see if you and your home are warm enough during cold weather

Homeless shelters

Community warming centers, safe and warm daytime locations where you can go during cold weather

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